U.S. patent application number 11/523973 was filed with the patent office on 2007-03-29 for apparatus and method for detecting fast feedback information in multi-cell base station in a broadband wireless communication system.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Joon-Young Bae, Jae-Ho Jeon, Seung-Joo Maeng, Ha-Young Yang.
Application Number | 20070071075 11/523973 |
Document ID | / |
Family ID | 37893890 |
Filed Date | 2007-03-29 |
United States Patent
Application |
20070071075 |
Kind Code |
A1 |
Yang; Ha-Young ; et
al. |
March 29, 2007 |
Apparatus and method for detecting fast feedback information in
multi-cell base station in a broadband wireless communication
system
Abstract
An apparatus and method for detecting a feedback signal in a
multi-cell or multi-sector sector BS in a broadband wireless
communication system are provided. A demodulator correlates each
tile being sets of subcarriers carrying feedback information
received from a serving sector/cell with each possible codeword and
calculates the squares of the absolute values of the correlations
of the tiles for each possible codeword. A first detection decider
sums the squares for each possible codeword and determines whether
to perform detection on the received feedback information. If it is
impossible to detect the feedback information, a second detection
decider receives feedback information from a target sector/cell,
combines the feedback information received from the serving
sector/cell and the target sector/cell, and determines whether to
detect the combined feedback information.
Inventors: |
Yang; Ha-Young; (Yongin-si,
KR) ; Bae; Joon-Young; (Seoul, KR) ; Jeon;
Jae-Ho; (Seongnam-si, KR) ; Maeng; Seung-Joo;
(Seongnam-si, KR) |
Correspondence
Address: |
DILWORTH & BARRESE, LLP
333 EARLE OVINGTON BLVD.
SUITE 702
UNIONDALE
NY
11553
US
|
Assignee: |
Samsung Electronics Co.,
Ltd.
Suwon-si
KR
|
Family ID: |
37893890 |
Appl. No.: |
11/523973 |
Filed: |
September 20, 2006 |
Current U.S.
Class: |
375/150 ;
375/260 |
Current CPC
Class: |
H04L 27/2647 20130101;
H04B 7/0417 20130101; H04B 7/0656 20130101 |
Class at
Publication: |
375/150 ;
375/260 |
International
Class: |
H04B 1/00 20060101
H04B001/00; H04K 1/10 20060101 H04K001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 2005 |
KR |
2005-0089869 |
Claims
1. An apparatus for detecting feedback information in a wireless
communication system, comprising: a demodulator for correlating
modulation symbols and pilot symbols included in each tile carrying
feedback information received from a serving sector for all
codewords, each tile being a set of subcarriers, and calculating
the squares of the absolute values of the correlations of the
tiles; a first detection decider for summing the squares of the
absolute values of the correlations of the tiles for all codewords,
and determining whether to perform detection on the received
feedback information based on the sums for the possible codewords;
and a second detection decider for receiving feedback information
from a target sector, combining the feedback information received
from the serving sector with the feedback information received from
the target sector, and determining whether to perform detection on
the combined feedback information.
2. The apparatus of claim 1, wherein the demodulator comprises: a
tile de-allocator for separating the tiles from the feedback
information received from the serving sector; and at least one
correlator for correlating the modulation symbols and pilot symbols
included in each tile with each possible codeword, and calculating
the squares of the absolute values of the correlations of the tiles
for each possible codeword
3. The apparatus of claim 2, wherein the number of correlators for
each tile is equal to the number of modulation symbols and pilot
symbols per tile.
4. The apparatus of claim 1, wherein the demodulator correlates the
modulation symbols and the pilot symbols on subcarriers of each
tile with symbols corresponding to an orthogonal vector for each
tile in each possible codeword and transmission pilot symbols.
5. The apparatus of claim 1, wherein the first detection decider
comprises: a codeword correlation calculator for summing the
squares of the absolute values of the correlations of the tiles for
each possible codeword and outputting the sums as first sums; and a
detection decider for comparing the difference between the maximum
of the first sums and the average of the first sums with a
threshold, and determining whether to perform detection on the
received feedback information based on the comparison.
6. The apparatus of claim 5, wherein the detection decider
determines that the feedback information received from the serving
sector is reliable if the difference is greater than or equal to
the threshold, and determines that the feedback information
received from the serving sector is not reliable and sends the
feedback information to the second detection decider if the
difference is less than the threshold.
7. The apparatus of claim 5, wherein the first detection decider
further comprises a calculator for calculating the
Carrier-to-Interference and Noise Ratio (CINR) of a codeword with
the maximum of the first sums, and wherein the detection decider
compares the CINR with a threshold and determines whether to
perform detection on the feedback information received from the
serving sector according to the comparison.
8. The apparatus of claim 1, wherein the second detection decider
starts to operate upon receipt of the feedback information from the
first detection decider.
9. The apparatus of claim 1, wherein the second detection decider
comprises: a combiner for, if it is impossible to detect the
feedback information received from the serving sector, receiving
the feedback information from the target sector, combining the
feedback information received from the serving sector with the
feedback information received from the target sector, calculating
the sum of the squares of the absolute values of the correlations
of the tiles in the combined feedback information for each possible
codeword, and outputting the sums for the possible codewords as
second sums; and a detection decider for comparing the difference
between the maximum of the second sums and the average of the
second sums with a threshold and determining whether to perform
detection on the feedback information received from the serving
sector and the target sector based on the comparison.
10. The apparatus of claim 9, wherein the detection decider
determines that the feedback information received from the serving
sector and the target sector is reliable if the difference is
greater than or equal to the threshold, and determines that the
feedback information received from the serving sector and the
target sector is not reliable and discards the feedback information
if the difference is less than the threshold.
11. The apparatus of claim 9, wherein the second detection decider
further comprises a calculator for calculating the CINR of a
codeword with the maximum of the second sums, and wherein the
detection decider compares the CINR with a threshold and determines
whether to perform detection on the feedback information received
from the serving sector and the target sector based on the
comparison.
12. The apparatus of claim 1, further comprising: a first detector
for detecting the feedback information received from the serving
sector if the first detection decider determines to perform
detection on the feedback information received from the serving
sector; and a second detector for detecting the feedback
information received from the serving sector and the target sector
if the second detection decider determines to perform detection on
the feedback information received from the serving sector and the
target sector.
13. A method of detecting feedback information in a wireless
communication system, comprising the steps of: determining whether
to perform detection on feedback information received from a
serving sector; receiving feedback information from a target
sector; and combining the feedback information received from the
serving sector with the feedback information received from the
target sector, and determining whether to perform detection on the
combined feedback information.
14. The method of claim 13, wherein the step of determining whether
to perform detection on feedback information received from a
serving sector comprises: separating tiles from the feedback
information received from the serving sector, each tile being a set
of subcarriers, correlating each tile carrying the feedback
information received from the serving sector with each possible
codeword, and calculating the squares of the absolute values of the
correlations of the tiles for each possible codeword; summing the
squares of the absolute values of the correlations of the tiles for
each possible codeword and outputting the sums for the possible
codewords as first sums; comparing the difference between the
maximum of the first sums and the average of the first sums with a
threshold; and determining that it is impossible to detect the
feedback information received from the serving sector if the
difference is less than the threshold.
15. The method of claim 14, further comprising the step of
performing detection on the feedback information received form the
serving sector if the difference is greater than or equal to the
threshold.
16. The method of claim 14, wherein the correlation step comprises
correlating modulation symbols and pilot symbols on subcarriers of
each tile with orthogonal vectors corresponding to each codeword
for each tile and transmission pilot symbols.
17. The method of claim 13, wherein the step of determining whether
to perform detection on the combined feedback information
comprises: calculating the sum of the squares of the absolute
values of the correlations of the tiles in the combined feedback
information for each possible codeword, and outputting the sums for
the possible codewords as second sums; comparing the difference
between the maximum of the second sums and the average of the
second sums with a threshold; and determining to perform detection
on the combined feedback information if the difference is greater
than or equal to the threshold.
18. The method of claim 17, further comprising determining that it
is impossible to detect the combined feedback information and
discarding the combined feedback information if the difference is
less than the threshold.
19. The method of claim 13, wherein the step of determining whether
to perform detection on feedback information received from a
serving sector comprises: separating tiles from the feedback
information received from the serving sector, each tile being a set
of subcarriers, correlating each tile carrying the feedback
information received from the serving sector with each possible
codeword, and calculating the squares of the absolute values of the
correlations of the tiles for each possible codeword; summing the
squares of the absolute values of the correlations of the tiles for
each possible codeword and outputting sums for the possible
codewords as first sums; calculating the Carrier-to-Interference
and Noise Ratio (CINR) of a codeword with the maximum of the first
sums and comparing the CINR with a threshold; and determining that
it is impossible to detect the feedback information received from
the serving sector if the CINR is less than the threshold.
20. The method of claim 19, further comprising performing detection
on the feedback information received form the serving sector if the
CINR is greater than or equal to the threshold.
21. The method of claim 19, wherein the CINR calculation step
comprises calculating the CINR of the codeword with the maximum of
the second sums using estimated signal power and noise power of the
codeword.
22. The method of claim 13, wherein the step of determining whether
to perform detection on the combined feedback information
comprises: calculating the sum of the squares of the absolute
values of the correlations of the tiles in the combined feedback
information for each possible codeword, and outputting the sums for
the possible codewords as second sums; calculating the CINR of a
codeword with the maximum of the second sums and comparing the CINR
with a threshold; and performing detection on the combined feedback
information if the CINR is greater than or equal to the
threshold.
23. The method of claim 22, further comprising determining that it
is impossible to detect the combined feedback information and
discarding the combined feedback information if the CINR is less
than the threshold.
24. An apparatus for detecting feedback information in a wireless
communication system, comprising: a demodulator for correlating
modulation symbols and pilot symbols included in each tile carrying
feedback information received from a serving cell for all
codewords, each tile being a set of subcarriers, and calculating
the squares of the absolute values of the correlations of the tiles
for all codeword; a first detection decider for summing the squares
of the absolute values of the correlations of the tiles for all
codewords, and determining whether to perform detection on the
received feedback information based on the sums for all the
codewords; and a second detection decider for receiving feedback
information from a target cell, combining the feedback information
received from the serving cell with the feedback information
received from the target cell, and determining whether to perform
detection on the combined feedback information.
25. The apparatus of claim 24, wherein the demodulator comprises: a
tile de-allocator for separating the tiles from the feedback
information received from the serving cell; and at least one
correlator for correlating the modulation symbols and pilot symbols
included in each tile with each possible codeword, and calculating
the squares of the absolute values of the correlations of the tiles
for each possible codeword
26. The apparatus of claim 25, wherein the number of correlators
for each tile is equal to the number of modulation symbols and
pilot symbols per tile.
27. The apparatus of claim 24, wherein the demodulator correlates
the modulation symbols and the pilot symbols on subcarriers of each
tile with symbols corresponding to an orthogonal vector for each
tile in each possible codeword and transmission pilot symbols.
28. The apparatus of claim 24, wherein the first detection decider
comprises: a codeword correlation calculator for summing the
squares of the absolute values of the correlations of the tiles for
each possible codeword and outputting the sums as first sums; and a
detection decider for comparing the difference between the maximum
of the first sums and the average of the first sums with a
threshold, and determining whether to perform detection on the
received feedback information based on the comparison.
29. The apparatus of claim 28, wherein the detection decider
determines that the feedback information received from the serving
cell is reliable if the difference is greater than or equal to the
threshold, and determines that the feedback information received
from the serving cell is not reliable and sends the feedback
information to the second detection decider if the difference is
less than the threshold.
30. The apparatus of claim 28, wherein the first detection decider
further comprises a calculator for calculating the
Carrier-to-Interference and Noise Ratio (CINR) of a codeword with
the maximum of the first sums, and wherein the detection decider
compares the CINR with a threshold and determines whether to
perform detection on the feedback information received from the
serving cell based on the comparison.
31. The apparatus of claim 24, wherein the second detection decider
starts to operate upon receipt of the feedback information from the
first detection decider.
32. The apparatus of claim 24, wherein the second detection decider
comprises: a combiner for, if it is impossible to detect the
feedback information received from the serving cell, receiving the
feedback information from the target cell, combining the feedback
information received from the serving cell with the feedback
information received from the target cell, calculating the sum of
the squares of the absolute values of the correlations of the tiles
in the combined feedback information for each possible codeword,
and outputting the sums for the possible codewords as second sums;
and a detection decider for comparing the difference between the
maximum of the second sums and the average of the second sums with
a threshold and determining whether to perform detection on the
feedback information received from the serving cell and the target
cell based on the comparison.
33. The apparatus of claim 32, wherein the detection decider
determines that the feedback information received from the serving
cell and the target cell is reliable if the difference is greater
than or equal to the threshold, and determines that the feedback
information received from the serving cell and the target cell is
not reliable and discards the feedback information if the
difference is less than the threshold.
34. The apparatus of claim 32, wherein the second detection decider
further comprises a calculator for calculating the CINR of a
codeword with the maximum of the second sums, and wherein the
detection decider compares the CINR with a threshold and determines
whether to perform detection on the feedback information received
from the serving cell and the target cell based on the
comparison.
35. The apparatus of claim 24, further comprising: a first detector
for detecting the feedback information received from the serving
cell if the first detection decider determines to perform detection
on the feedback information received from the serving cell; and a
second detector for detecting the feedback information received
from the serving cell and the target cell if the second detection
decider determines to perform detection on the feedback information
received from the serving cell and the target cell.
36. A method of detecting feedback information in a wireless
communication system, comprising the steps of: determining whether
to perform detection on feedback information received from a
serving cell; receiving feedback information from a target cell;
and combining the feedback information received from the serving
cell with the feedback information received from the target cell
when receiving the feedback information from the target cell, and
determining whether to perform detection on the combined feedback
information.
37. The method of claim 36, wherein the step of determining whether
to perform detection on feedback information received from a
serving cell comprises: separating tiles from the feedback
information received from the serving cell, each tile being a set
of subcarriers, correlating each tile carrying the feedback
information received from the serving cell with each possible
codeword, and calculating the squares of the absolute values of the
correlations of the tiles for each possible codeword; summing the
squares of the absolute values of the correlations of the tiles for
each possible codeword and outputting the sums for the possible
codewords as first sums; comparing the difference between the
maximum of the first sums and the average of the first sums with a
threshold; and determining that it is impossible to detect the
feedback information received from the serving cell if the
difference is less than the threshold.
38. The method of claim 37, further comprising performing detection
on the feedback information received form the serving cell if the
difference is greater than or equal to the threshold.
39. The method of claim 37, wherein the correlation step comprises
correlating modulation symbols and pilot symbols on subcarriers of
each tile with symbols corresponding to an orthogonal vector for
each tile in each possible codeword and transmission pilot
symbols.
40. The method of claim 36, wherein the step of determining whether
to perform detection on the combined feedback information
comprises: calculating the sum of the squares of the absolute
values of the correlations of the tiles in the combined feedback
information for each possible codeword, and outputting the sums for
the possible codewords as second sums; comparing the difference
between the maximum of the second sums and the average of the
second sums with a threshold; and determining to perform detection
on the combined feedback information if the difference is greater
than or equal to the threshold.
41. The method of claim 40, further comprising determining that it
is impossible to detect the combined feedback information and
discarding the combined feedback information if the difference is
less than the threshold.
42. The method of claim 36, wherein the step of determining whether
to perform detection on feedback information received from a
serving cell comprises: separating tiles from the feedback
information received from the serving cell, each tile being a set
of subcarriers, correlating each tile carrying the feedback
information received from the serving cell with each possible
codeword, and calculating the squares of the absolute values of the
correlations of the tiles for each possible codeword; summing the
squares of the absolute values of the correlations of the tiles for
each possible codeword and outputting sums for the possible
codewords as first sums; calculating the Carrier-to-Interference
and Noise Ratio (CINR) of a codeword with the maximum of the first
sums and comparing the CINR with a threshold; and determining that
it is impossible to detect the feedback information received from
the serving cell if the CINR is less than the threshold.
43. The method of claim 42, further comprising performing detection
on the feedback information received form the serving cell if the
CINR is greater than or equal to the threshold.
44. The method of claim 42, wherein the CINR calculation step
comprises calculating the CINR of the codeword with the maximum of
the second sums using estimated signal power and noise power of the
codeword.
45. The method of claim 36, wherein the step of determining whether
to perform detection on the combined feedback information
comprises: calculating the sum of the squares of the absolute
values of the correlations of the tiles in the combined feedback
information for each possible codeword, and outputting the sums for
the possible codewords as second sums; calculating the CINR of a
codeword with the maximum of the second sums and comparing the CINR
with a predetermined threshold; and performing detection on the
combined feedback information if the CINR is greater than or equal
to the threshold.
46. The method of claim 45, further comprising determining that it
is impossible to detect the combined feedback information and
discarding the combined feedback information if the CINR is less
than the threshold.
47. An apparatus for detecting feedback information in a wireless
communication system, comprising: a demodulator for correlating
modulation symbols and pilot symbols with orthogonal vectors
corresponding to codewords and the transmitted pilot symbols
respectively; and a channel decoder for summing the squares of the
absolute values of the correlations of the tiles for each codeword,
and combining the feedback information received from the serving
sector with the feedback information received from the target
sector, and determining whether to perform detection on the
combined feedback information.
Description
PRIORITY
[0001] This application claims priority under 35 U.S.C. .sctn. 119
to an application entitled "Apparatus and Method for Detecting Fast
Feedback Information in Multi-Cell Base Station in a Broadband
Wireless Communication System" filed in the Korean Intellectual
Property Office on Sep. 27, 2005 and assigned Serial No.
2005-89869, the contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to an apparatus and
method for detecting feedback information in a broadband wireless
communication system, and in particular, to an apparatus and method
for detecting uplink fast feedback information in a multi-cell or
multi-sector Base Station (BS) in a broadband wireless
communication system.
[0004] 2. Description of the Related Art
[0005] In a high-speed mobile communication system, a BS schedules
packet data transmission and determines transmission parameters
using uplink fast feedback information representing downlink
channel quality, in order to provide a high-speed packet data
service to Mobile Stations (MSs). Upon receipt of the uplink fast
feedback signals from the MSs, the BS checks the downlink channel
statuses to the MSs based on the feedback information. The BS then
selects MSs having the best downlink channel quality according to
the channel status information in every slot and sends packet data
to the selected MSs. The BS also determines transmission parameters
(e.g. data rate, code rate, and modulation order) according to the
downlink channel quality of the selected MSs. The uplink fast
feedback information may include a Signal-to-Noise Ratio (SNR), a
Carrier-to-Interference Ratio (C/I), the differential SNR of each
band, a fast Multiple Input Multiple Output (MIMO) feedback, or a
mode selection feedback. Additional physical channels are
configured for delivering the uplink fast feedback information in a
communication system, for example an Orthogonal Frequency Division
Multiple Access (OFDMA) communication system.
[0006] The BS uses C/Is measured at the MSs in determining the
downlink channel quality. The MSs measure C/Is and feed back the
C/I measurements to the BS on physical channels, e.g. Channel
Quality Indicator CHannels (CQICHs). The BS schedules downlink data
for the MSs and determines transmission parameters based on the C/I
measurements.
[0007] The C/I information, by which downlink data rates and cell
throughput are determined, has to be sent with high reliability
despite its small size, because it is very critical to the
operation of the communication system. Yet, it is typical not to
allocate much time-frequency resources to the physical channels
carrying the fast feedback information in order to reduce an
overhead rate. Accordingly, there exists a need for an efficient
detection method to enable reliable transmission.
[0008] FIG. 1 is a flowchart illustrating a conventional feedback
information detecting operation. The following description is based
on the assumption that each tile is defined by 3.times.3
subcarriers and an MS feeds back 4-bit information data.
[0009] Referring to FIG. 1, a BS monitors reception of an uplink
fast feedback signal in step 101. Upon receipt of the feedback
signal, the BS converts the received time-domain feedback signal to
a frequency signal by Fast Fourier Transform (FFT) in step 103.
[0010] In step 105, the BS separates tiles from the FFT feedback
signal, correlates modulation symbols on eight subcarriers in each
of the tiles with an orthogonal vector corresponding to the tile in
each codeword, and squares the absolute value of the correlation of
the tile.
[0011] The BS then sums the squares of the absolute values of the
correlations of six tiles for each of 16 possible codewords,
selects the maximum (MAX) of the sums, and calculates the average
(AVG) of the sums with respect to the 16 codewords in step 107.
[0012] In step 109, the BS compares the difference between the
maximum and the average with a predetermined threshold (Th). If the
difference is less than the threshold ((MAX-AVG)<Th), the BS
discards the feedback signal without performing detection,
determining that the feedback signal is not reliable in step
113.
[0013] On the other hand, if the difference between the maximum and
the average is greater than or equal to the threshold
((MAX-AVG).gtoreq.Th), the BS performs detection, taking into
consideration that the information data of the codeword with the
maximum is reliable in step 111. Then the BS ends the
algorithm.
[0014] FIGS. 2 and 3 illustrate codewords that can be generated
from an M-ary channel encoder.
[0015] FIG. 2 is a table listing 2.sup.4 (=16) codewords that can
be generated from 4-bit information data, and FIG. 3 is a table
listing 2.sup.6 (=64) codewords that can be generated from 6-bit
information data.
[0016] FIG. 4 illustrates orthogonal vectors used for orthogonal
modulation of the codewords of FIGS. 2 and 3. P .times. .times. 0
.times. ( exp .function. ( j .times. .pi. 4 ) ) , P .times. .times.
1 .times. ( exp .function. ( j .times. 3 .times. .pi. 4 ) ) , P
.times. .times. 2 .times. ( exp .function. ( - j .times. 3 .times.
.pi. 4 ) ) , and .times. .times. P .times. .times. 3 .times. ( exp
.function. ( - j .times. .pi. 4 ) ) ##EQU1## are Quadrature Phase
Shift Keying (QPSK) symbols. Pilot symbols, which are known to both
the BS and the MS, are generally multiplied by a scrambling code
and modulated in Binary Phase Shift Keying (BPSK).
[0017] As described above, an uplink subchannel carries uplink fast
feedback information. Conventionally, information bits are
determined using only a fast feedback signal received in a serving
BS managing a corresponding cell or sector. Therefore, in case
where the uplink fast feedback information is scattered due to some
obstacle and thus received in a target cell, detection of the fast
feedback information suffers from information loss.
SUMMARY OF THE INVENTION
[0018] An aspect of the present invention is to substantially solve
at least the above problems and/or disadvantages and to provide at
least the advantages below. Accordingly, an aspect of the present
invention is to provide an apparatus and method for efficiently
detecting uplink fast feedback information using time-frequency
resources in a multi-cell or multi-sector BS in a broadband
wireless communication system.
[0019] Another aspect of the present invention is to provide an
apparatus and method for efficiently detecting uplink fast feedback
information using uplink fast feedback information received in a
target cell or sector of a multi-cell or multi-sector BS as well as
uplink fast feedback information received in a serving cell or
sector of the multi-cell or multi-sector BS.
[0020] The above aspects are achieved by providing an apparatus and
method for detecting a feedback signal in a multi-cell or
multi-sector sector BS in a broadband wireless communication
system
[0021] According to one aspect of the present invention, in an
apparatus for detecting a feedback signal in a multi-sector BS in a
broadband wireless communication system, a demodulator correlates
modulation symbols and pilot symbols included in each tile carrying
feedback information received from a serving sector with each
possible codeword, and calculates the squares of the absolute
values of the correlations of the tiles for each possible codeword.
Each tile is a set of subcarriers. A first detection decider sums
the squares of the absolute values of the correlations of the tiles
for each possible codeword, and determines whether to perform
detection on the received feedback information according to the
sums for the possible codewords. If it is impossible to detect the
feedback information received from the serving sector, a second
detection decider receives feedback information from a target
sector, combines the feedback information received from the serving
sector with the feedback information received from the target
sector, and determines whether to perform detection on the combined
feedback information.
[0022] According to another aspect of the present invention, in a
method of detecting feedback information in a multi-sector BS in a
broadband wireless communication system, it is determined whether
to perform detection on feedback information received from a
serving sector. If it is impossible to detect the feedback
information received from the serving sector, reception of feedback
information from a target sector is monitored. Upon receipt of the
feedback information from the target sector, the feedback
information received from the serving sector is combined with the
feedback information received from the target sector, and it is
determined whether to perform detection on the combined feedback
information.
[0023] According to a further aspect of the present invention, in
an apparatus for detecting a feedback signal in a multi-cell BS in
a broadband wireless communication system, a demodulator correlates
modulation symbols and pilot symbols included in each tile carrying
feedback information received from a serving cell with each
possible codeword, and calculates the squares of the absolute
values of the correlations of the tiles for each possible codeword.
Each tile is a set of subcarriers. A first detection decider sums
the squares of the absolute values of the correlations of the tiles
for each possible codeword, and determines whether to perform
detection on the received feedback information according to the
sums for the possible codewords. If it is impossible to detect the
feedback information received from the serving cell, a second
detection decider receives feedback information from a target cell,
combines the feedback information received from the serving cell
with the feedback information received from the target cell, and
determines whether to perform detection on the combined feedback
information.
[0024] According to still another aspect of the present invention,
in a method of detecting feedback information in a multi-cell BS in
a broadband wireless communication system, it is determined whether
to perform detection on feedback information received from a
serving cell. If it is impossible to detect the feedback
information received from the serving cell, reception of feedback
information from a target cell is monitored. Upon receipt of the
feedback information from the target cell, the feedback information
received from the serving cell is combined with the feedback
information received from the target cell, and it is determined
whether to perform detection on the combined feedback
information.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The above and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description when taken in conjunction with the
accompanying drawings in which:
[0026] FIG. 1 is a flowchart illustrating a conventional feedback
information detecting operation;
[0027] FIG. 2 illustrates a table of typical codewords that can be
output from a channel encoder, for the input of 4-bit information
data;
[0028] FIG. 3 illustrates a table of typical codewords that can be
output from the channel encoder, for the input of 6-bit information
data;
[0029] FIG. 4 illustrates a table of typical orthogonal vectors for
use in modulation;
[0030] FIG. 5 illustrates an uplink fast feedback signal received
in a multi-cell BS according to the present invention;
[0031] FIG. 6 is a block diagram of the multi-cell BS for receiving
feedback information according to the present invention;
[0032] FIG. 7 is a block diagram of an apparatus for determining
detection of feedback information in the BS according to the
present invention,
[0033] FIG. 8 is a flowchart illustrating a feedback information
detecting operation according to the present invention; and
[0034] FIG. 9 is a flowchart illustrating a feedback information
detecting operation according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Preferred embodiments of the present invention will be
described herein below with reference to the accompanying drawings.
In the following description, well-known functions or constructions
are not described in detail since they would obscure the invention
in unnecessary detail.
[0036] The present invention provides a technique for detecting
uplink fast feedback information in a multi-cell or multi-sector BS
using uplink fast feedback information received in a target cell or
sector as well as uplink fast feedback information received in a
serving cell or sector. The multi-cell or multi-sector BS is a BS
that simultaneously covers multiple cells or sectors. When each
cell or sector has one processing module, the multi-cell or
multi-sector BS combines signals received from the cells or sectors
by connecting interfaces among them. In the case of one processing
module per multi-cell or multi-sector BS, a modem can be
implemented in software to combine signals received from the cells
or sectors in the multi-cell or multi-sector BS.
[0037] The following description is made in the context of an OFDMA
broadband wireless communication system and also in the context of
a multi-sector structure. The same description applies to a
multi-cell structure.
[0038] FIG. 5 illustrates an uplink fast feedback signal received
in a multi-sector BS according to the present invention.
[0039] Referring to FIG. 5, when an MS 503 within a serving sector
505 of a multi-sector BS 501 sends an uplink fast feedback signal
to the BS 501, the feedback signal is scattered by reflection and
thus propagated to target sectors 507 and 509 as well a to the
serving sector 505. According to the present invention, the
feedback signal received in the serving sector is combined with the
reflected signals received in the target sectors in order to
perform data detection efficiently with less information loss.
[0040] FIG. 6 is a block diagram of the multi-sector BS for
receiving feedback information according to the present
invention.
[0041] Referring to FIG. 6, the BS includes a Radio Frequency (RF)
processor 601, an Analog-to-Digital Converter (ADC) 603, a Fast
Fourier Transform (FFT) processor 605, a non-coherent demodulator
607, and a channel decoder 609.
[0042] The RF processor 601 downconverts an RF signal of feedback
information received through an antenna to a baseband analog
signal. The ADC 603 converts the analog signal to a digital signal.
The FFT processor 605 converts time sample data received from the
ADC 603 to frequency data by FFT.
[0043] The non-coherent demodulator 607 calculates soft-decision
values of the FFT symbols by non-coherent demodulation. The channel
decoder 609 determines the reliability of the received feedback
information based on the soft-decision values. If the feedback
information is reliable, the soft-decision values are decoded at a
predetermined code rate, a codeword corresponding to the
soft-decision values is determined, and data of the codeword is
demodulated.
[0044] If the feedback information is received in the serving
sector, the channel decoder 609 receives a decoded fast feedback
signal from a target sector, combines the feedback signals of the
serving sector and the target sector, and determines the
reliability of the feedback signal again, which will be described
in detail with reference to FIG. 7.
[0045] FIG. 7 is a block diagram of an apparatus for determining
detection of feedback information in the BS according to the
present invention. The following description is based on the
assumption that each tile is defined by 3.times.3 subcarriers and
4-bit information data is used.
[0046] Referring to FIG. 7, in the BS, the non-coherent demodulator
607 includes a tile de-allocator 701 and correlators 703 to 706.
The channel decoder 609 includes a codeword arranger 707, detection
deciders 713 and 719, detectors 715 and 721, and an adder 717.
[0047] The tile de-allocator 701 separates six tiles each including
3.times.3 subcarriers from the FFT symbols received from the FFT
processor 605 illustrated in FIG. 6. For example, when one
subchannel is composed of six tiles, the six tiles are separated
from the subchannel.
[0048] The correlators 703 to 706 correlate the subcarriers (i.e.
tones) of each of the tiles with each codeword and squares the
absolute value of the correlation. Specifically, a received
3.times.3 subcarrier set (tile) with modulation symbols on eight
subcarriers and a pilot symbol on one subcarrier is correlated with
a 3.times.3 subcarrier set with symbols corresponding to an
orthogonal vector in a codeword and a pilot transmission
symbol.
[0049] The codeword arranger 707 sums the squares of the absolute
values of the correlations of the tiles for each of 16 codewords
(codeword 0 to codeword 15) through adders 709 to 711. Then the
codeword arranger 707 calculates the average of the sums with
respect to the 16 codewords.
[0050] The first detection decider 713 selects the maximum of the
sums received from the codeword arrangers 707 and compares the
difference between the maximum and the average with a threshold,
thereby determining whether to detect the feedback information.
[0051] If the difference between the maximum and the average is
greater than or equal to the threshold ((MAX-AVG).gtoreq.Th), the
first detection decider 713 sends the feedback information to the
first detector 715, considering that the received feedback
information is reliable. The first detector 715 detects the
feedback information.
[0052] On the other hand, if the difference is less than the
threshold ((MAX-AVG)<Th), the first detection decider 713
considers that the reception environment of the feedback signal is
poor and outputs the feedback signal to the adder 717, so that the
feedback signal is detected using a feedback signal received in the
target sector.
[0053] For every possible codeword, the adder 717 adds the sum of
the squares of the absolute values of the correlations of the
feedback signal received from the first detection decider 713 to
the sum of the squares of the absolute values of the correlations
of a feedback signal received from the target sector. The feedback
signal from the MS within the serving sector is scattered under a
channel environment and then reaches to the target sector. Thus,
the target sector calculates the sum of the squares of the absolute
values of the correlations of the feedback signal with respect to
every possible codeword. Since the target sector has knowledge of
the environment of the serving sector (e.g. information about slots
allocated to the MS), it can carry out the correlation.
[0054] The second detection decider 719 selects the maximum
(MAX.sub.SUM) of the sums received from the adder 717 and
calculates the average (AVG.sub.SUM) of the sums with respect to
all the codewords. Then the second detection decider 719 compares
the difference between the maximum sum and the average sum with a
threshold, thereby determining whether to detect the feedback
information.
[0055] If the difference between the maximum sum and the average
sum is greater than or equal to the threshold
((MAX.sub.SUM-AVG.sub.SUM).gtoreq.Th), the second detection decider
719 sends the combination between the received feedback signal and
the feedback signal received in the target sector to the second
detector 721, considering that the combined feedback information is
reliable. The second detector 719 detects the combined feedback
information.
[0056] On the other hand, if the difference is less than the
threshold ((MAX-AVG)<Th), the second detection decider 719
discards the feedback signal, considering that the reception
environment of the feedback signal is poor.
[0057] In the above-described embodiment, each of the first and
second detection deciders 713 and 719 determines whether to detect
the feedback signal by comparing the difference between MAX and AVG
(or the difference between MAX.sub.SUM and AVG.sub.SUM) with the
threshold. It can be further contemplated as another embodiment
that each of the first and second detection deciders 713 and 719
calculates the Carrier-to-Interference and Noise Ratio (CINR) of
MAX (or MAX.sub.SUM) and determines whether to detect the feedback
signal by comparing the CINR with a threshold.
[0058] FIG. 8 is a flowchart illustrating a feedback information
detecting operation according to the present invention.
[0059] Referring to FIG. 8, the BS monitors reception of an uplink
fast feedback signal from a serving sector in step 801. Upon
receipt of the feedback signal, the BS converts the received
time-domain feedback signal to a frequency signal by FFT in step
803.
[0060] In step 805, the BS separates tiles from the FFT feedback
signal, correlates modulation symbols on eight subcarriers and a
pilot symbol on one subcarrier in each of the tiles with an
orthogonal vector corresponding to the tile in every possible
codeword and a transmission pilot symbol, and squares the absolute
values of the correlations of the tiles for the codeword.
[0061] The BS sums the squares of the absolute values of the
correlations of the tiles, for every codeword, selects the maximum
(MAX) of the sums, and calculates the average (AVG) of the sums in
step 807.
[0062] In step 809, the BS compares the difference between the
maximum and the average with a threshold (Th). If the difference
between the maximum and the average is greater than or equal to the
threshold ((MAX-AVG).gtoreq.Th), the BS performs detection,
considering that the received feedback information is reliable in
step 819.
[0063] If the difference is less than the threshold
((MAX-AVG)<Th), the BS monitors reception of the sum of the
squares of the absolute values of the correlations of the tiles
carrying feedback information received in a target sector with
every possible codeword from the target sector in step 811. The
feedback signal from the MS within the serving sector is scattered
under a channel environment and then reaches to the target sector.
Thus, the target sector calculates the sum of the squares of the
absolute values of the correlations of the feedback signal with
respect to every possible codeword. Since the target sector has
knowledge of the environment of the serving sector (e.g.
information about slots allocated to the MS), it can carry out the
correlation.
[0064] In step 813, for every possible codeword, the BS adds the
sum of the squares of the absolute values of the correlations of
the feedback signal received from the serving sector to the sum of
the squares of the absolute values of the correlations of a
feedback signal received from the target sector. The BS selects the
maximum (MAX.sub.SUM) of the sums and calculates the average
(AVG.sub.SUM) of the sums with respect to the 16 codewords.
[0065] In step 815, the BS compares the difference between the
maximum sum and the average sum with a threshold (Th). If the
difference between the maximum sum and the average sum is greater
than or equal to the threshold
((MAX.sub.SUM-AVG.sub.SUM).gtoreq.Th), the BS performs detection,
considering that information data corresponding to a codeword with
the maximum sum is reliable. Then the BS ends the algorithm.
[0066] If the difference is less than the threshold
((MAX-AVG)<Th), the BS discards the feedback signal without
detection, considering that the feedback signal is not reliable in
step 817. Then the BS ends the algorithm.
[0067] FIG. 9 is a flowchart illustrating a feedback information
detecting operation according to another embodiment of the present
invention.
[0068] Referring to FIG. 9, the BS monitors reception of an uplink
fast feedback signal from a serving sector in step 901. Upon
receipt of the feedback signal, the BS converts the received
time-domain feedback signal to a frequency signal by FFT in step
903.
[0069] In step 905, the BS separates tiles from the FFT feedback
signal, correlates modulation symbols on eight subcarriers and a
pilot symbol on one subcarrier in each of the tiles with an
orthogonal vector corresponding to the tile in every possible
codeword and a transmission pilot symbol, and squares the absolute
values of the correlations of the tiles for the codeword.
[0070] The BS sums the squares of the absolute values of the
correlations of the tiles, for every codeword and selects a
codeword with the maximum (MAX) of the sums in step 907.
[0071] The BS calculates the CINR of the feedback signal by
estimating the transmit power and noise power of the feedback
signal using the selected codeword in step 909. In step 911, the BS
compares the CINR with a threshold (Th).
[0072] If the CINR is greater than or equal to the threshold
(CINR.gtoreq.Th), the BS performs detection, considering that
information data corresponding to the codeword with the maximum is
reliable in step 923.
[0073] If the CINR is less than the threshold (CINR<Th), the BS
monitors reception of the sum of the squares of the absolute values
of the correlations of the tiles carrying feedback information
received in a target sector with every possible codeword from the
target sector in step 913. The feedback signal from the MS within
the serving sector is scattered under a channel environment and
then reaches to the target sector. Thus, the target sector
calculates the sum of the squares of the absolute values of the
correlations of the feedback signal with respect to every possible
codeword. Since the target sector has knowledge of the environment
of the serving sector (e.g. information about slots allocated to
the MS), it can carry out the correlation.
[0074] In step 915, for every possible codeword, the BS adds the
sum of the squares of the absolute values of the correlations of
the feedback signal received from the serving sector to the sum of
the squares of the absolute values of the correlations of a
feedback signal received from the target sector; The BS selects a
codeword with the maximum (MAX.sub.SUM) of the sums.
[0075] In step 917, the BS calculates the CINR (CINR.sub.SUM) of
the feedback signal by estimating the transmit power and noise
power of the feedback signal using the selected codeword. The BS
compares the CINR with a predetermined threshold (Th) in step
919.
[0076] If the CINR is greater than or equal to the threshold
(CINR.sub.SUM.gtoreq.Th), the BS performs detection, considering
that information data corresponding to the codeword with the
maximum is reliable in step 923.
[0077] If the CINR is less than the threshold (CINR.sub.SUM<Th),
the BS discards the feedback signal, considering that the feedback
signal is not reliable in step 921. The BS then ends the
algorithm.
[0078] The above description has bee made in the context of a
multi-sector BS. If more than one BS is simultaneously supported, a
diversity gain can be achieved from a combination of the fast
feedback signals from the BSs as well as from a combination of the
fast feedback signals from the cells.
[0079] In accordance with the present invention as described above,
uplink feedback information from an MS is detected using uplink
fast feedback information from a target cell or sector as well as
uplink fast feedback information from a serving cell or sector in a
multi-cell or multi-sector BS in an OFDMA broadband wireless
communication system. Therefore, accurate information transmission
and stable system operation are achieved. Also, since the feedback
information detection scheme is applicable irrespective of a
subchannel structure, a tile structure, the number of bits in
information data, and the number of receive antennas, the system
operation is rendered flexible.
[0080] While the invention has been shown and described with
reference to certain preferred embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims.
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